With the development of new, relatively air-stable transition metal carbene complex catalysts—particularly ones exhibiting increased tolerance towards common organic functional groups—the olefin metathesis reaction has established itself as one of the most powerful reactions in the synthetic preparation of alkenes.
Ruthenium carbene complexes—for example, the “first-generation” and “second generation” Grubbs-type catalysts developed by Nobel laureate Robert H. Grubbs—are especially popular and versatile catalysts for use in olefin metathesis. The polymeric di-μ-chloro(η4-1,5-cyclooctadiene)ruthenium(II)—represented herein as [RuCl2(COD)]x—and the monomeric tris(triphenylphosphine)ruthenium(II) chloride—represented herein as RuCl2(PPh3)3—are precursors in the synthesis of ruthenium carbene complexes.
As shown in FIG. 1, [RuCl2(COD)]x (Inorganic Syntheses, 1989, 29, 68-77) and RuCl2(PPh3)3 (Inorganic Syntheses, 1970, 12, 237-240) are typically prepared starting from RuCl3.nH2O. The ruthenium trichloride is itself prepared starting from ruthenium refinery salts (e.g., salts of ruthenium-halo complexes produced in the refining of natural platinum group metal deposits and recycled platinum group metals). However, since the ruthenium refinery salts are first converted to ruthenium metal, which in turn is then oxidized to Ru(III), the preparations of [RuCl2(COD)]x and RuCl2(PPh3)3 via the intermediacy of ruthenium trichloride are costly and inefficient.
A more efficient and less costly preparation of [RuCl2(COD)]x, RuCl2(PPh3)3, and analogous MX2Lq ruthenium carbene complex precursors from ruthenium refinery salts—particularly one that does not require the intermediacy of ruthenium metal and/or ruthenium trichloride—is desirable.